DRK is the fast tank so don't see GUN being a fast tank that identity is already taken. DPS wise we have WAR so that's already used up. It would make more sense for GUN to be a energy tank that works to compliment the other three tanks or benefits for the DPS or healers. So far the tanks with the best synergy has been WAR and PLD which has left DRK out but with GUN it can be more creative